In conventional oil and gas operations, a well is typically drilled to a desired depth with a drill string, which includes drill pipe and a drilling bottom hole assembly (BHA). Once the desired depth is reached, the drill string is removed from the hole and casing is run into the vacant hole. In some conventional operations, the casing may be installed as part of the drilling process. A technique that involves running casing at the same time the well is being drilled may be referred to as “casing-while-drilling.”
Casing may be defined as pipe or tubular that is placed in a well to prevent the well from caving in, to contain fluids, and to assist with efficient extraction of product. When the casing is properly positioned within a hole or well, the casing is typically cemented in place by pumping cement through the casing and into an annulus formed between the casing and the hole (e.g., a wellbore or parent casing). The cement may fill all or a portion of the casing such that an initial amount of cement is forced, by the accumulated head of cement and/or pumping pressure, out of the bottom of the casing and up along the outside diameter of the casing such that the cement passes into the annulus between the casing and the hole. It then becomes desirable to push substantially all of the cement out of the casing and further into the annulus to cement the casing in place. Accordingly, once a sufficient amount of cement has been poured into the casing, the cement may be forced out of the interior of the casing and into the annulus by pushing a plug through the casing with pressurized displacement fluid.
Once a easing string has been positioned and cemented in place or installed, the process may be repeated via the now installed casing string. For example, the well may be drilled further by passing a drilling BHA through the installed casing string and drilling. Further, additional casing strings may be subsequently passed through the installed casing string (during or after drilling) for installation. Indeed, numerous levels of casing may be employed in a well. For example, once a first string of casing is in place, the well may be drilled further and another string of casing (an inner string of casing) with an outside diameter that is accommodated by the inside diameter of the previously installed casing may be run through the existing casing. Additional strings of casing may be added in this manner such that numerous concentric strings of casing are positioned in the well, and such that each inner string of casing extends deeper that the previously installed casing or parent casing string.
Liner may also be employed in some drilling operations. Liner may be defined as a string of pipe or tubular that is used to case open hole below existing casing. Casing is generally considered to extend all the way back to a wellhead assembly at the surface. In contrast, a liner merely extends a certain distance (e.g., 30 meters) into the previously installed casing or parent casing string. However, a tieback string of casing may be installed that extends from the wellhead downward into engagement with previously installed liner. The liner is typically secured to the parent casing string by a liner hanger that is coupled to the liner and engages with the interior of the upper casing or liner. The liner hanger may include a slip device (e.g., a device with teeth or other gripping features) that engages the interior of the upper casing string to hold the liner in place. It should be noted that, in some operations, a liner may extend from a previously installed liner or parent liner.
Again, the distinction between casing and liner is that casing generally extends all the way to the wellhead and liner only extends to a parent casing or liner. Accordingly, the terms “casing” and “liner” may be used interchangeably in the present disclosure. Indeed, liner is essentially made up of similar components (e.g., strings of tubular structures) as casing. Further, as with casing, a liner is typically cemented into the well. A cementation assembly is typically employed at the end of a pipe string to facilitate cementation of a liner. Traditional cementation assemblies sting into the top of a liner and enable injection of cement into the liner from the surface via the pipe string. As with the cementation of the casing discussed above, the cement may be forced through the liner such that it exits a bottom of the liner and fills the annulus between the liner and the hole. Thus, the liner may be cemented into the well.
It is now recognized that existing techniques for the cementation of liners into wells may result in a lack of consistency in the cement disposed in the annulus formed by the liner and the well. Accordingly, it is now recognized that improved techniques and equipment for cementing liners into wells are desirable.